DICYANATE POLYMER

Polystyrene modified dicyanate polymer was obtained by simultaneous polymerization of styrene monomer and BPA/DC. The handling of low viscous dicyanate solution in styrene is more convenient that the processing of crystalline BPA/DC or high-viscous dicyanate prepolymers [52]. A similar patent specification describes the polymerization of a mixture of styrene, BPA/DC and p-isopropenyl cyanate BMI (cf. Sect. 5) was also used [53]. 

Woo Woo, E. M., Shimp, D. A., Seferis, J. C. Phase stmcture and toughening mechanisms of a thermoplastic-modified aryl dicyanate. Polymer 35 (1994) 1658-1665. 

A new polymer type which emerged as important materials for circuit hoards are polycyanurates. The simplest monomer is the dicyanate ester of hisphenol A. When polymerized, it forms three-dimensional, densly cross-linked structures through three-way cyanuric acid (2,4,6-triazinetriol) ... 

Continuity can also be reached by polymerizing one of the components within the other. In such a case the blend is called an IPN, an interpenetrating network it is, in most cases formed by a thermoset in a thermoplastic polymer. An example is a compound built-up from 50% of a thermoplast (polycarbonate or polysulphone), and 50% of a cross-linked polymer on the basis of dicyanate bisphenol-A. The skeleton... 

In addition to the high-pressure polycondensation reactions mentioned above, we have studied the high-pressure polyaddition for the synthesis of high-temperature aromatic polymers such as polyaminoimide from bismaleimide and aromatic diamine, polycyanurates from aromatic dicyanates, and polyiso-cyanurates from aromatic diisocyanates [34,36-40]. 

This latter method is interesting since a linear polymer is obtained, contraryly to the direct trimerization of dicyanated compounds. 

As a result of the trimerization of dicyanates, crosslinked polymers consisting of benzene and triazine rings are formed (Scheme 3). 

Among the patents and patent applications concerning the uses of dicyanates in polymer technology, the information prevails on systems which consist of dicyanates and other monomers and polymers. Although such systems are the object of this article, the polymer materials obtained solely from aromatic dicyanates are reviewed shortly, too, in order to present a more complete set of information. 

Poly addition of dicyanates with various bifunctional monomers leads to linear, branched or crosslinked polymer [3],... 

From BPA/DC and pyromellitic dianhydride, linear polyimidocarbamates were synthesized [27-29]. For the same purpose, various dicyanates and tetracarboxylic acid dianhydrides were used [29-31]. If one of the starting monomers has a functionality higher than 2, crosslinked polymers are obtained,... 

Dicyanates react with diisocyanates. The poly addition results in the formation of crosslinked polymers with cyanurate and isocyanurate rings [32]. The polymers have high deformation and decomposition temperature in the case of a crosslinked copolymer from 9,9-bis(4-cyanatophenyl)fluorene the corresponding values are 480 °C and 440 °C (in air), respectively. 

Linear polymers were obtained by the polyaddition of dicyanates with the compounds, which contain active protons primary and secondary amines, glycols and bisphenols. The reaction with diamines given polyisoureas [30, 31] (Scheme 8). 

The linear addition copolymers of dicyanates are synthesized at equimolecular ratio of the comonomers. If one of the comonomers is used in excess, lower-molecular-weight polymers with corresponding end groups are obtained, which can further react with chain elongation agents. Terminal cyanate groups can be cyclotrimerized to obtain crosslinked polymers. 

The reaction of dicyanates and bismaleimides leads to crosslinked polymers (Scheme 10). Separate trimerization of the dicyanate and radical polymerization of bismaleimide can also occur, thus forming an IPN. 

A variety of CEs with tailorable physico-chemical and thermo-mechanical properties have been synthesized by appropriate selection of the precursor phenol [39,40]. The physical characteristics like melting point and processing window, dielectric characteristics, environmental stability, and thermo-mechanical characteristics largely depend on the backbone structure. Several cyanate ester systems bearing elements such as P, S, F, Br, etc. have been reported [39-41,45-47]. Mainly three approaches can be seen. While dicyanate esters are based on simple diphenols, cyanate telechelics are derived from phenol telechelic polymers whose basic properties are dictated by the backbone structure. The terminal cyanate groups serve as crosslinking sites. The polycyanate esters are obtained by cyanation of polyhydric polymers which, in turn, are synthesized by suitable synthesis protocols. Thus, in addition to the bisphenol-based CEs, other types like cyanate esters of novolacs [37,48], polystyrene [49], resorcinol [36], tert-butyl, and cyano substituted phenols [50], poly cyanate esters with hydrophobic cycloaliphatic backbone [51], and allyl-functionalized cyanate esters [52] have been reported. 

Several polymers were synthesized to initiate the development of this concept (30). In one case (single amino acid), poly(palmitoyl-hydroxypro-line [(Pal-Hpr)-ester] was obtained by melt transesterification of Af-Pal-Hpr-Me in the presence of aluminum isopropoxide as catalyst. In a second case (dipeptide), the tyrosine (Tyr) dipeptide carbobenzyoxy-Tyr-Tyr-Hex was cyanylated at the tyrosine side chain hydroxyl groups, to yield car-bobenzoxy-Tyr-Tyr-Hex-dicyanate. By solution polymerization of equimolar quantities of carbobenzoxy-Tyr-Tyr-Hex and carbobenzoxy-Tyr-Tyr-Hex-dicyanate in tetrahydrofuran, poly(carbobenzoxy-Tyr-Tyr-Hex-iminocarbonate) (polyCTTH) was obtained with Mn = 11,500 and Mw = 19,500. 

Iron-arene complexes are known to exhibit extremely high photoactivity as initiators. Quantum efficiencies have been found to be greater than I in the photopolymerisation of dicyanate esters. Phenylglycine derivatives have been found to be excellent co-synergists for the iron-arene complexes when used in conjunction with dyes and amines. Complexes of various types have also been proposed. Maleic anhydride-THF complexes have been used for the photopolymerisation of oligourethane acrylates while metal-ion complexes of spiropyran copolymers undergo reversible polymer precipitation. Azo and polyazo initiators have been used to make butadiene-isoprene block copolymers while charge-transfer complexes of morpholine-chlorine induce the radical polymerisation of methyl methacrylate. The presence of zinc chloride enhances the... 

Cyanate esters are a family of aryl dicyanate monomers that contain the reactive cyanate (-0-C=N) fimctional group. When heated, this cyanate functionality undergoes an exothermic cyclotrimerization reaction to form triazine ring connecting units, resulting in the formation of a thermoset polycyanate polymer. 

Kim Kim, Y.-S., Kim, S.-C. Properties of polyetherimide/dicyanate semi-interpenetrating polymer network having the morphology spectrum. Macromolecules 32 (1999) 2334-2341. 

OlHar Harismendy, L, del Rio, M., Marieta, C., Gavalda, J., Mondragon, I. Dicyanate ester-po-lyetherimide semi-interpenetrating polymer networks. II. Effects of morphology on the fracture toughness and mechanical properties. J. Appl. Polym. Sci. 80 (2001) 2759-2767. 

Oxamidrazone, NHj—NH—C(NH)—C(NH)—NH—NH2, is produced from dicyan and hydrazine, and its isomer converted with terephthaloyl chloride to poly(terephthaloyl oxamidrazone), PTO. PTO can be converted to a poly(triazole), a poly(oxadiazole), or to a metal ion chelated polymer ... 

Cyanate/Cyanurate. When aryl cyanate esters are heated to 150 to 250°C, they cyclotrimerize to cyanuric acid esters (Fig. 3.62). They can be catalyzed by organo-metallic and active hydrogen compounds. When the monomer is a dicyanate such as bisphenol A dicyanate (Fig. 3.63), the result is a highly cross-linked heterocyclic polymer (Table 3.57). Using a novolac polycyanate has produced Tg and useful life over 300°C. 

Those studies were extended to include the addition of an organic montmoril-lonite nanoscale filler to the polysulfone/dicyanate mixture (Mondragon et al. 2006). The primary reason for the introduction of the filler is the significant improvement in properties that can be obtained at low clay contents. The exfoliated configuration for the clay is of particular interest in that regard because it maximizes the interactions, making the entire surface of the clay layers available for interactions with the polymer matrix. This should lead to dramatic changes in both mechanical and physical properties. 

This reaction has been used to synthesize polyimides (more properly polyimide carbamates) from dianhydrides and dicyanates [23]. The reaction proceeds in nitrobenzene at high temperature, catalysed by triethylamine. The thermal resistance of these polymers is much lower than that of pure aromatic polyimides, and, therefore, the reaction has not found practical application. 

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